1. Field of the Invention
This invention generally relates to scanners using light to read coded symbologies of varying reflectivity. More particularly, the invention pertains to scanners having rotating mirror wheels in the path of the laser light used to detect and read coded symbologies. Most particularly, the invention pertains to laser scanners having simplified optics for emitting and collecting the light used to read coded symbologies in near to medium focal ranges.
2. Description of the Prior Art
Coded symbologies, such as bar coded symbols, are well known. Coded symbols generally use light and dark areas of varying size in specified combinations. Each unique combination of light and dark areas represents encoded information. Coded symbology scanners read the code by passing a beam of light over it, collecting information in the form of light reflected back from the code, and decoding the collected information.
Prior art bar code scanners can be divided into two main categories, coaxial and non-coaxial. U.S. Pat. No. 5,028,772 is an example of a coaxial bar code reader. In this patent, a laser emits a beam of light which ultimately passes through an apertured mirror to a facet on a rotating polygon. The beam reflects off the facet through a second series of mirrors and towards a target surface. The light beam reflects off the target surface as diffused light. The diffused light passes back through the second series of mirrors towards a facet. The diffused light reflects off the facet towards the apertured mirror. All of the reflected light, except that which passes through the aperture, is directed towards a lens which focuses it onto a photo detector. Since the emitted light beam and the returned light follow the same path or axis, this scanner is referred to as coaxial. Coaxial scanners are particularly useful in reading surfaces at long focal lengths. During manufacture, coaxial scanners require testing and fine tuning to insure proper alignment of the laser, mirrors, polygon, lens and detector.
U.S. Pat. No. 5,262,628 is an example of a non-coaxial bar code reader. A laser emits a beam of light which is guided by a mirror towards a facet on a rotating polygon. The beam reflects off the facet towards the object. Upon striking the object, diffused light reflects off the surface. A detector is positioned at the front of the scanner to collect the diffused light. In this scanner, the emitted light beam and the detected light follow two distinct paths or axis. One axis is through the polygon to the surface. The other is from the surface directly to the detector. There is no attempt or means for focusing the diffused light on the detector. This scanner is referred to as non-coaxial.
Another example of a non-coaxial scanner is U.S. Pat. No. 3,813,140. The laser emits a beam of light directly towards a facet of the polygon. The beam reflects off the facet towards the target. The light reflected from the target is diffused and returns along a different axis to another facet of the polygon. This facet directs the diffused light towards a mirror. The mirror guides the diffused light towards a detector.
U.S. Pat. No. 4,115,703 is another example of non-coaxial scanner. The laser emits a beam of light directly at the surface to be scanned. The light reflects off the surface and passes through an aperture in the scanner located directly above the target area. The returned light passes through a lens barrel to a photo detector. To read a code, the scanner must be manually moved across the entire code. Non-coaxial scanners are inexpensive and effective at short focal lengths. At longer focal lengths, non-coaxial scanners are not as effective due to ambient light reaching the detector.
There exists a need for an inexpensive scanner that can scan at near to medium focal lengths of up to two feet from the target area.
The present invention provides an inexpensive scanner that can scan at near to medium focal lengths. A light beam is generated to illuminate a target area on the scanned object. A mirrored surface directs the light beam towards the object and light reflected from the object to a detector. The detector is positioned to receive a constant amount of reflected light from the mirrored surface.